This invention refers to boron trichloride and more particularly to a method of forming boron trichloride in a molten salt bath.
The prior art teaches various methods of manufacturing boron trichloride which include, for example, melting the reactants and bringing them together at a relatively high temperature. Specifically, Wood in British Pat. No. 832,096 teaches that boron trihalides ae obtained by the reaction in the molten state of boron oxide with alkali metal halides and that the interaction is preferably carried out at 800.degree. to 1000.degree. C.
Bikofsky et al, U.S. Pat. No. 3,206,283, teach that boron trichloride can be manufactured by reacting at high temperatures, the halide of a basic metal (e.g. CaF.sub.2) with an anhydrous metal borate salt in the presence of silica. It is indicated that typically the reactants are heated at a temperature range from 1100.degree. to 1600.degree. C to effect the reaction.
British Pat. No. 887,400 recites a process for producing boron trichloride by reaction of carbon, chlorine and boron anhydride which may be formed in situ from the acid by dehydration which comprises passing chlorine gas through a mixture of boric anhydride, carbon and sodium tetraborate at a temperature at which the mixture is in a molten state which is generally a temperature in the range of 800.degree. to 1100.degree. C.
While the foregoing process apparently satisfactorily produce BCl.sub.3 from a molten bath, they all require relatively high operating temperatures, i.e. 800.degree. and above. It is known in the art however to produce BCl.sub.3 at a lower temperature using a fluidized bed. Thus, Kratel et al, U.S. Pat. No. 3,839,538, teach the formation of boron trichloride by the reaction of alkaline earth metal borides with anhydrous hydrogen halides in a fluidized bed. The reaction is effected by passing a hydrogen halide through a fluidized bed of a heated alkaline earth metal boride. However, this process can result in small particles and dust being entrained with the reaction gases from the reactor necessitating a further separation step. This requirement can result in the production of boron trichloride being uneconomical.
Thus, a need exists for a low temperature method of producing boron trichloride in a molten bath, thus avoiding the dust problem of fluidized bed production without requiring as much energy as the molten systems in the prior art.